Surge suppression for current limiting circuits

ABSTRACT

A limiting circuit for controlling overshoot in a charge current in a battery recharging system includes a current amplifier receiving input indicative of charge current in a rechargeable battery circuit and generating a current error signal, a voltage amplifier receiving input indicative of charge voltage in the rechargeable battery circuit and generating a voltage error signal, and a power amplifier receiving a first signal indicative of power in a switching voltage regulator and a second power signal indicative of power in the rechargeable battery circuit, and generating a power error signal. The limiting circuit compares the voltage error signal, the current error signal, and the power error signal to determine the error signal having the greatest value, and generates an input signal to a pulse width modulation comparator. The limiting circuit also includes an internal current source, a first transistor coupled to the current amplifier, a second transistor coupled to the voltage amplifier; and a third transistor coupled to the power amplifier. The first transistor, the second transistor, and the third transistor are coupled to the internal current source to determine the error signal having the greatest value. To prevent reverse current flow in the switching voltage regulator, a low current comparator receives a signal indicative of the current flowing in the switching voltage regulator, and generates an output signal. A transistor receives the output signal from the low current comparator, and generates a signal to maintain the current flowing in the switching regulator circuit above a threshold value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of portable battery equipment, andmore particularly, to a method and apparatus for charging portablebatteries using synchronous rectification.

2. Description of the Related Art

To improve customer satisfaction with portable battery operatedequipment, in particular notebook computers, it is desired to re-chargebatteries as quickly as possible. The amount of time required to chargea battery depends on the chemical process as well as the battery chargerpower processing efficiency.

Re-chargers for portable batteries utilize switching regulators toregulate DC power input from a DC voltage source such as a battery or anAC to DC adapter. Switching regulators are typically classified intodifferent configurations or “topologies.” One such topology is thesingle-ended inductor circuit, consisting of relatively simple circuitswhere a switch determines whether the voltage applied to an inductor isthe input voltage, V_(dc), or zero. In this manner, the output voltageis a function of the average voltage applied to the inductor. The switchmay be implemented using various electronic components, for example, apower transistor, coupled either in series or parallel with the load.The regulator controls the turning ON and turning OFF of the switch inorder to regulate the flow of power to the load. The switching regulatoremploys inductive energy storage elements to convert the switchedcurrent pulses into a steady load current. Power in a switchingregulator is thus transmitted across the switch in discrete currentpulses.

In order to generate a stream of current pulses, switching regulatorstypically include control circuitry to turn the switch on and off. Theswitch duty cycle, which controls the flow of power to the load, can bevaried by a variety of methods. For example, the duty cycle can bevaried by either (1) fixing the pulse stream frequency and varying theON or OFF time of each pulse, or (2) fixing the ON or OFF time of eachpulse and varying the pulse stream frequency. Which ever method is usedto control the duty cycle, the switch in switching regulators is eitherOFF, where no power is dissipated by the switch, or ON in a lowimpedance state, where a small amount of power is dissipated by theswitch. This generally results in fairly efficient operation with regardto the average amount of power dissipated.

One method that has been utilized to improve operational efficiency ofvoltage regulators employs synchronous rectification. In synchronousrectification, a pair of switches, which are connected in series betweenthe input voltage and ground, are synchronized so that either the inputvoltage or ground is applied to the input of an inductor. Thesynchronous control of the switches provides improved efficiencycompared to traditional circuits which employed a switch and a diode.

Certain switching regulators with synchronous rectification provide apositive output voltage, however, current can flow out of, or into theregulator's output. When input voltage is removed while current isflowing into the regulator's output, energy stored in the inductor willbe discharged, creating excess voltage in the circuit. This over-voltagecondition frequently results in destruction of circuit components.

There are several ways to prevent damage from reverse current. U.S. Pat.No. 5,731,694 issued to Wilcox et al. teaches a method and circuit forcontrolling reverse current in switching regulators with synchronousrectification. The Wilcox et al. patent optimizes protection during lowload current efficiency but does not pertain to battery chargingapplications. Further, when power is removed and then reapplied to theWilcox et al. device, the current overshoots a steady state value. Inbattery charging applications, this overshoot can cause undesirableoscillations in protection circuits, where a protection switch istripped ON and OFF for several seconds. The oscillations result in pulsecharging which greatly lowers the efficiency of the charging process.Additionally, the current overshoot decreases the useful life of batterycharger components, which are fabricated with graphite having a latticestructure that breaks down when exposed to over-current conditions.

In view of the foregoing, it is desirable to provide a switchingregulator with synchronous rectification for use in a battery recharger,wherein the switching regulator includes a control circuit which reducesor substantially eliminates current overshoot.

SUMMARY OF THE INVENTION

In one embodiment, the present invention pertains to a computer systemwherein a rechargeable battery circuit supplies power to a centralprocessing unit, and the power is dissipated from battery cells in thebattery circuit as the power is supplied to the central processing unit.A battery recharger includes a switching voltage regulator circuit thatsupplies current and voltage to recharge the rechargeable batterycircuit. The rechargeable battery circuit determines when a faultcondition is present in the battery cells and opens a charging switch toprevent the current and voltage supplied by the switching voltageregulator from being applied to the battery cells. When the faultcondition is cleared and the charging switch closes, a limiting circuitgenerates a control signal to prevent the current from overshooting asteady state value. The limiting circuit utilizes a limiting function,such as a ramp function as input to a pulse width modulation comparator.

Another feature of the present invention is to provide a currentamplifier in the limiting circuit that receives a current signal fromthe battery circuit and generates a current error signal that is inputto the pulse width modulation comparator.

A further feature of the present invention is to provide a voltageamplifier in the limiting circuit that receives a voltage signal fromthe battery circuit and generates a voltage error signal, a currentamplifier that receives a current signal from the battery circuit andgenerates a current error signal, and a power amplifier that receives apower signal from the battery circuit and generates a power errorsignal. The limiting circuit compares the voltage error signal, thecurrent error signal, and the power error signal, and inputs the errorsignal having the greatest value to the pulse width modulationcomparator.

In order to compare the error signals, a further feature of the limitingcircuit includes an internal current source, a first transistor coupledto the current amplifier, a second transistor coupled to the voltageamplifier, and a third transistor coupled to the power amplifier. Thefirst transistor, the second transistor, and the third transistor arecoupled to the internal current source to determine the error signalhaving the greatest value.

Another feature of the present invention is to have a computer systemwhich prevents reverse current flow in the switching voltage regulatorby including a low current comparator that receives a signal indicativeof the current flowing in the switching voltage regulator and generatesan output signal, a transistor having a base coupled to receive theoutput signal from the low current comparator and to provide an inputsignal to a pulse width modulation comparator, wherein input signalmaintains the current flowing in the switching regulator circuit above athreshold value.

In an alternative embodiment, an additional feature of the presentinvention is to provide an apparatus for controlling charge current in abattery recharging system. The apparatus includes a current amplifierreceiving input indicative of charge current in a rechargeable batterycircuit, and generating a current error signal, and a pulse widthmodulation comparator receiving a first input signal from a limitingfunction and a second input signal based on the current error signal.

A further feature of the present invention is to provide a voltageamplifier receiving input indicative of charge voltage in therechargeable battery circuit, generating a voltage error signal, andoutputting the voltage error signal to the pulse width modulationcomparator.

A further feature of the present invention is to provide a poweramplifier receiving a first power signal indicative of power in theswitching voltage regulator and a second power signal indicative ofpower in the rechargeable battery circuit, generating a power errorsignal, and outputting the power error signal to the pulse widthmodulation comparator.

A further feature of the present invention is to provide a limitingcircuit that compares the voltage error signal, the current errorsignal, and the power error signal to determine the error signal havingthe greatest value, and to generate an input signal to the pulse widthmodulation comparator based on the error signal having the greatestvalue.

A further feature of the present invention is to provide a limitingcircuit that includes an internal current source, a first transistorcoupled to the current amplifier, a second transistor coupled to thevoltage amplifier; and a third transistor coupled to the poweramplifier. The first transistor, the second transistor, and the thirdtransistor are coupled to the internal current source to determine theerror signal having the greatest value.

An additional feature of the present invention is to provide a limitingcircuit that includes a low current comparator receiving a signalindicative of the current flowing in the switching voltage regulator,and generating an output signal, and a transistor coupled to receive theoutput signal from the low current comparator, and to generate a signalto maintain the current flowing in the switching regulator circuit abovea threshold value.

In another embodiment, an additional feature of the present invention isto provide a method for controlling charge current in a batteryrecharging system wherein the battery recharging system includes aswitching voltage regulator circuit coupled to a rechargeable batterycircuit having a plurality of battery cells. The method includes: (a)determining when excess voltage is present in the battery cells; (b)opening a charge switch in the rechargeable battery circuit to preventcharge current from flowing to the battery cells when excess voltage ispresent the battery cells; (c) comparing current output by the switchingvoltage regulator circuit to charge current in the rechargeable batterycircuit; and (d) limiting the current output by the switching voltageregulator to prevent overshoot in the charge current after the chargeswitch recloses.

An additional feature of the present invention is to provide a methodfor controlling charge current in a battery recharging system thatfurther includes: (a) generating a voltage error signal based on thevoltage output by the switching voltage regulator and charge voltage inthe rechargeable battery circuit; (b) generating a current error signalbased on the current flowing through a portion of the switching voltageregulator and charge current in the rechargeable battery circuit; (c)generating a power error signal based on the power input to theswitching voltage regulator and charge power in the rechargeable batterycircuit; (d) comparing the voltage error signal, the current errorsignal, and the power error signal to determine the error signal havingthe greatest value; and (e) limiting the current output by the switchingvoltage regulator based on the error signal having the greatest value.

The foregoing has outlined rather broadly the objects, features, andtechnical advantages of the present invention so that the detaileddescription of the invention that follows may be better understood.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1 is a schematic block diagram of a prior art switching regulatorcircuit employing a switch including a pair of synchronously-switchedMOSFETs in a step-down configuration;

FIG. 2A is a time history diagram showing gate voltage at one MOSFETswitch of the prior art switching regulator circuit of FIG. 1;

FIG. 2B is a time history diagram showing gate voltage at another MOSFETswitch of the prior art switching regulator circuit of FIG. 1;

FIG. 2C is a time history diagram showing inductor current in the priorart switching regulator circuit of FIG. 1;

FIG. 3 is a time history diagram of output current in the prior artswitching regulator circuit of FIG. 1;

FIG. 4 is a schematic block diagram of a battery monitoring and controlcircuit internal to a battery pack;

FIG. 5 is a schematic block diagram of a switching regulator circuitwith synchronous rectification incorporating reverse current protectionand current overshoot control circuits; and

FIG. 6 is a time history diagram of inductor current from a batterycharger incorporating reverse current protection and current overshootcontrol according to the present invention during a pulse charge event.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

Referring to FIG. 1, a schematic block diagram of a switching regulatorcircuit 100 found in the prior art for providing a regulated DC outputvoltage V_(o) to drive a load which, for example, may be a portable orlaptop computer or other battery-operated system, is shown having aswitch including a pair of synchronously-switched MOSFETs 102 (Q1) and104 (Q2), diodes 106 (D1), 108 (D2), 110 (D3), inductor 112 (L1),capacitor 114 (C1), resistors 116 (R7), 118 (R9) and 120 (R10), currentamplifier 122, over-current comparator 124, zero current detector 126,driver control circuit 128, high side driver circuit 130, low sidedriver circuit 132, and AND gate 134.

Switching regulator circuit 100 operates from an unregulated DC supplyvoltage V_(dc) in couple to a terminal, e.g., a battery (not shown).Note that the DC source may be derived from the output of an AC adapter,or by other conventional means. The output voltage V_(o) is the averagevoltage applied to inductor 112. conductor 112 and capacitor 114 smooththe alternating supply of current to provide regulated voltage V_(o).The alternating sequence of open and close actions by switching MOSFETs102 and 104 regulates the voltage such that the longer switching MOSFETs102 and 104 are closed, the higher the regulated voltage (because ahigher average current flows through inductor 112). In order to supplythe alternating current, MOSFETS 102 and 104 are respectively driven byhigh side driver 130 and low side driver 132, which in turn are bothcontrolled by driver control circuit 128. Delay mechanisms, such asdiodes 108 and 110, are incorporated in switching regulator circuit 100to ensure that one MOSFET turns OFF before the other turns ON. FIGS. 2athrough 2 c show examples of time history graphs of pulse waveformoutput signals from high side driver 130 and low side driver 132 andtime history of peak to peak current through inductor 112, respectively.

Driver control circuit 128 receives input signals including pulse widthmodulated (PWM) signal 136, clock signal 138, and over-current signal139. Based on the input signals, driver control circuit 128 outputs anOFF pulse of constant duration (e.g., 2 to 10 microseconds) during whichtime MOSFET 104 is held OFF and MOSFET 102 is held ON by high sidedriver 130 and low side driver 132 respectively. Otherwise, drivercontrol circuit 128 provides an ON pulse during which time MOSFET 104 isheld ON and MOSFET 102 is held OFF. Thus, driver control circuit 128alternately turns MOSFETS 102 and 104 ON and OFF to provide analternating supply of current. The duty cycle of the driver controlcircuit 128 is controlled based on pulse width modulated (PWM) signal136, clock signal 138, and over-current signal 139.

Inductor current I_(L) is sensed by sampling resistor 120 and input tocurrent amplifier 122. Resistors 116 and 120 scale voltage to generateinput to current amplifier 122. Over-current comparator 124 receivescurrent error signal 142 from current amplifier 122 and referenceover-current signal 140. Over-current comparator 124 thus limits, orclamps, current transients by decreasing output voltage V_(o). FIG. 2shows a time history diagram of the inductor current I_(L) of switchingregulator circuit 100. At time T_(off), input voltage V_(dc) is cut off,and at time T_(on), input voltage V_(dc) is resumed. Such a cutoff ofinput voltage may occur, for example, when a protective circuit shutsoff V_(dc) due to a power over supply being delivered to the devicedriven by switching regulator circuit 100. If the protective circuitdetermines that the over supply condition has abated and that powershould be supplied, it resumes supplying input voltage V_(dc), denotedby time T_(on). Inductor current I_(L) ramps up to an overshoot valuethat is determined by the time constant of switching regulator circuit100 and the value of the reference over-current signal 140. During thetime period that I_(L) overshoots its steady state value, current errorsignal 142 is greater than reference over-current signal 140.Accordingly, over-current signal 139 is HIGH, causing driver controlcircuit 128 to reduce the amount of time MOSFETs 102 and 104 are ONuntil current error signal 142 is less than reference over-currentsignal 140.

When MOSFET 102 is turned OFF by high side driver 130 and MOSFET 104 isturned ON by low side driver 132, inductor current I_(L) begins to rampdown. During low average inductor currents, this current may ramp downtowards zero and may eventually go negative, changing polarity ofinductor 112. Zero current detector 126 monitors inductor current I_(L)by way of current error signal 142. When current error signal 142 isgreater than reference current signal 144, output signal 146 from zerocurrent detector 126 goes LOW and turns OFF MOSFET 104 by way of ANDgate 134. Turning OFF MOSFET 104 prevents current reversals in inductorcurrent I_(L) from drawing power from the load to ground through MOSFET104. MOSFET 104 also prevents circuit 100 from becoming a voltage boostcircuit instead of a buck circuit, wherein the increased voltagesproduced by the boost circuit would damage electronic components incircuit 100. After MOSFET 104 is turned OFF, it will again be allowed toturn ON as soon as current error signal 142 is less than referencecurrent signal 144 to cause output signal 146 to go HIGH. Thus,switching regulator circuit 100 includes circuitry for intentionallyholding MOSFET 104 OFF during periods when current reversals wouldotherwise allow power to be drawn from the load.

Disadvantages of the prior art switching regulator circuit 100 arisewhen it is utilized with a battery circuit 400 such as shown in FIG. 4.Output voltage V_(o) from switching regulator 100 is input to batterycircuit 400 and supplies power for recharging battery cells 402. Suchbattery cells 402 may be constructed of various materials includinglithium ion battery cells. In certain battery recharging systems, it isdesirable to provide protective circuitry to prevent overchargingconditions. Battery circuit 400 includes microcontroller 404 todischarge switch 406 and charge switch 408, each shown in FIG. 4 asincluding a MOSFET and a diode connected in parallel. Microcontroller404 controls the ON/OFF state of discharge switch 406 and charge switch408 to prevent switching regulator circuit 100 output voltage V_(o) frombeing applied to battery cells 402 when certain conditions are detectedby microcontroller 404.

Inputs supplied to microcontroller 404 are generated utilizing currentsense resistor 410, current amplifier 412, voltage amplifier 414,multiplexer 416, and backup protection circuit 418 including secondprotector circuit 420 and fuse 422. Current amplifier 412 receivessignals indicative of the current flowing through current sense resistor410 and outputs a scaled value of the current as current signal 424 tomicrocontroller 404. Microcontroller 404 utilizes the current signal tomonitor the flow of current through battery circuit 400 and the properoperation of discharge switch 406 and charge switch 408. Multiplexer 416and second protector circuit 420 receive signals indicative of thevoltage across battery cells 402. Multiplexer 416 outputs a series ofsignals indicative of the voltage across individual battery cells 402 tovoltage amplifier 414. Voltage amplifier 414 outputs scaled values ofthe voltage across each battery cell 402 to microcontroller 404. Secondprotector circuit 420 and microcontroller 404 utilize the voltagesignals to monitor the voltage of each cell and detect overvoltageconditions.

The disadvantages of utilizing the prior art switching regulator circuit100 with battery circuit 400 arise when the absolute value of anybattery cell is greater than an upper limit and protection logic in themicrocontroller 404 opens charge switch 408 to prevent the flow ofcharge current I_(c). When the open circuit voltage falls below a lowerlimit, microcontroller 404 closes charge switch 408 and charge currentI_(c) is allowed to flow to battery cells 402. If the charge currentI_(c) is allowed to overshoot when charge is resumed, as shown in FIG.3, then the excess current causes the voltage in the battery cell toexceed the upper limit and an oscillatory condition results between theovershoot current and protection logic in microcontroller 404. Thisoscillation causes repeated opening and closing of charge switch 408,and results in pulse charging of the battery. The pulse charging lowersthe efficiency of the charging process and increases the amount of timerequired to charge battery cells 402. The value of the overshoot currentmay also violate battery charging specifications.

FIG. 5 shows a schematic diagram of an embodiment of a switching voltageregulator 500 incorporating the present invention for limiting circuit502 for detecting and preventing reverse current flow and overshootcurrent when battery charging is resumed. For purposes of illustration,the present limiting circuit 502 is shown coupled to prior art switchingvoltage regulator 100. Note, however, that the principles embodied inlimiting circuit 502 may be applied to prevent overshoot in othervoltage regulators, and the present invention is not intended to belimited in application to switching voltage regulator 100.

In order to prevent current overshoot, limiting circuit 502 uses power,voltage, and current feedback to limit the charging voltage V_(c).Limiting circuit 502 is coupled to microcontroller 404 in batterycircuit 400 via system management bus 504 to receive battery data signal506 and system time data signal 508. Logic is included in systemmanagement bus 504 to generate battery cell voltages signal 510, chargecurrent signal 512, and charge power signal 514. Voltage, current, andpower digital to analog converters (DACs) 516, 518, 520 convert digitalvoltage, current, and power signals 510, 512, and 514 to analog signalsthat are input to voltage amplifier 522, current amplifier 524, andpower amplifier 526, respectively, as feedback reference signals.Voltage amplifier 522 generates a voltage error signal based on outputvoltage V_(o) from switching voltage regulator 100 and the voltage inbattery circuit 400. Current amplifier 524 generates a current errorsignal based on current error signal 142 and the current in batterycircuit 400. Power amplifier 526 generates a power error signal based onpower input to switching voltage regulator 100 and the power in batterycircuit 400. Amplifiers 522, 524, and 526 may be one of severalcommercially available amplifiers such as transconductance amplifiers.Other embodiments of the present invention may be utilized wherein oneor two of the error signals are generated.

To regulate the current output by switching voltage regulator 100, thebase of each transistor 528, 530, and 532 is coupled to receive voltage,current, and power error signals (in units of volts) output byamplifiers 522, 524, and 526, respectively. Transistors 528, 530, and532 are coupled to constant current source 534 in a manner that wiresthe emitters of transistors 528, 530, and 532 in an OR configuration andpulls them up to current source 534. The dominant, or largest, signalbetween the output signals of the voltage amplifier 522, currentamplifier 524, and power amplifier 526 is input to pulse widthmodulation (PWM) comparator 538 to provide an error voltage signal 536.Correspondingly fewer transistors are required in embodiments of thepresent invention that generate only one or two of the error signals.

When the value of a limiting function, such as a ramp input 540 to PWMcomparator 538 is greater than error voltage signal 536 from currentsource 534, PWM output signal 136 is HIGH. When the error voltage signal536 from current source 534 is greater than the signal from ramp input540, PWM output signal 136 is LOW. PWM output signal 136 is input todriver control circuit 128 in switching voltage regulator 100. The errorvoltage signal 536 and ramp input 540 thus determine the duty cycle ofthe driver control circuit 128 so that the output current I_(o) andtherefore, the charge current I_(c), approaches the steady state currentvalue with little or no overshoot as shown in FIG. 6. Note that thelimiting function, shown as ramp input 540, may generate other types oflimiting input instead of ramp input 540.

In addition to preventing current overshoot, limiting circuit 502includes low current comparator 560, capacitor 562, transistor 564 andresistors 566, 568 to prevent reverse current flow in switching voltageregulator 100 as follows. When the output from current amplifier 524 isgreater than the output from voltage amplifier 532 and power amplifier526, and a steady charge current I_(c) is present in battery circuit400, low current comparator 560 is held HIGH at a predetermined currentthreshold, such as 100 milliamps. When charge current I_(c) isinterrupted, such as by an overcharge condition in battery circuit 400,or when the charge current I_(c) falls below the predetermined currentthreshold, the output of low current comparator 560 transitions LOW, andthe output current I_(o) is clamped by transistor 564 and resistor 566to a predetermined value, such as 200 milliamps. When microcontroller404 opens charge switch 408, current control registers are programmed toprovide a constant charge current I_(c), for example, of 4 amps. In thissituation, the output of voltage amplifier 522 will control the outputof PWM comparator 538, providing a constant output voltage V_(o). Thus,current is not allowed to fall below the threshold of transistor 564,thereby preventing reverse current in switching voltage regulator 100.When charge switch 408 is closed, output current I_(o) is clamped bytransistor 564 at the predetermined value. When charge current signal512 crosses the predetermined current threshold, low current comparator560 transitions HIGH. The voltage at the base of transistor 564 slowlyrises due to the time constant of resistor 568 and capacitor 562. Therising base voltage of transistor 564 increases emitter current oftransistor 564, and the output voltage of current amplifier 524gradually increases.

The embodiment of the present invention shown in FIG. 5 utilizeshardware components such as amplifiers 522, 524, and 526, comparators538 and 560, transistors 528, 530, 532, and 564, to implement thecontrol circuitry for determining when to limit the current and voltagesupplied by the switching voltage regulator 100 to battery circuit 400.The present invention may be implemented using alternative components.For example, limiting circuit 502 could be any device capable ofreceiving signals from battery circuit 400 and switching voltageregulator 100, generating a control signal, such as PWM signal 136, andinputting the signal to switching voltage regulator 100. One such devicecould be a microcontroller utilizing hardware, software, and/or firmwareto read in the signals from DACS 516, 518, and 520, and provide a signalwhich is utilized to regulate the duty cycle of high side driver 130 andlow side driver 132. Thus, it should be understood that the presentinvention provides a system for limiting charge current and/or chargevoltage in a battery circuit, such as battery circuit 400, to preventthe charge current from overshooting a steady state value, and tofurther prevent reverse current from flowing through a voltage regulatorin the system, such as switch power regulator 100.

While the invention has been described with respect to the embodimentsand variations set forth above, these embodiments and variations areillustrative and the invention is not to be considered limited in scopeto these embodiments and variations. Accordingly, various otherembodiments and modifications and improvements not described herein maybe within the spirit and scope of the present invention, as defined bythe following claims.

What is claimed:
 1. A surge protection circuit for protecting volatileelectronic components from data loss comprising: a current limiterhaving an input voltage coupled to an input supply voltage to aperipheral and the current limiter having an output voltage; a currentsource coupled to the input supply voltage providing an additionalsource of current for a limited period of time such that the inputvoltage does not fall below a level causing volatile data to be lost;and a current rate limiting circuit reducing the rate of flow of currentto the peripheral device and having a first terminal coupled to theoutput voltage of the current limiter and the current rate limitingcircuit having a second terminal available as an output load voltagesuch that the rate of flow of current is inversely proportional to theadditional source of current during a loop response time.
 2. The surgeprotection circuit of claim 1, wherein the current limiter is acommercially available integrated circuit device.
 3. The surgeprotection circuit of claim 1, wherein the current source is a capacitorand the current rate limiting circuit is an inductor, such that the sizeof the capacitor is inversely proportional to the size of the inductor.4. The surge protection circuit of claim 1, further comprising: a firstclamping diode having a first terminal coupled to the first terminal ofthe current rate limiting circuit and the clamping diode having a secondterminal coupled to the input supply voltage; and a second clampingdiode having a first terminal coupled to the first terminal of thecurrent rate limiting circuit and the second clamping diode having asecond terminal coupled to ground.
 5. A method of suppressing currentsurges comprising: providing a source of current to a load from an inputsupply voltage to a peripheral; limiting the source of current andreducing the rate of flow of current from the input supply voltageprovided to the load to a set output current level such that when thesource of current from the input supply voltage exceeds the set outputcurrent level the source of current from the input supply voltage islimited to the set output current level after a loop response time;opposing a rapid change in the rate of flow of current from the inputsupply voltage to the load; and providing an additional source ofcurrent to the load for a limited period of time such that the provisionof the source of current to the load from the input supply voltageduring the rapid change in the rate of flow of current does not causethe input supply voltage to drop below a minimum necessary voltage levelto prevent data loss in volatile electronic components such that therate of flow of current is inversely proportional to the additionalsource of current during the loop response time.
 6. A computer systemhaving a surge protection circuit for protecting volatile electroniccomponents from data loss due to voltage variances, the computer systemcomprising: a system bus; at least one microprocessor connected toaccess the system bus; one or more peripherals, each connected to accessthe system bus; a means for attaching one or more additional peripheralsto access the system bus wherein a peripheral load voltage is suppliedto the one or more additional peripherals; a power supply for supplyingan input supply voltage to the computer system; a surge protectioncircuit for preventing the input supply voltage from dropping to a levelwhich causes volatile data to be lost when attaching the one or moreadditional peripherals to the system bus comprising: a current limiterhaving an input voltage coupled to the input supply voltage and thecurrent limiter having an output voltage; a current source coupled tothe input supply voltage providing an additional source of current for alimited period of time such that the input supply voltage does not fallbelow a level causing volatile data to be lost; and a current ratelimiting circuit reducing the rate of flow of current to a peripheraldevice and having a first terminal coupled to the output voltage of thecurrent limiter and the current rate limiting circuit having a secondterminal connected to the peripheral load voltage such that the rate offlow of current is inversely proportional to the additional source ofcurrent during a loop response time.
 7. The computer system of claim 6,wherein the current limiter is a commercially available integratedcircuit device.
 8. The computer system of claim 6, wherein the currentsource is a capacitor and the current rate limiting circuit is aninductor, such that the size of the capacitor is inversely proportionalto the size of the inductor.
 9. The computer system of claim 6, furthercomprising: a first clamping diode having a first terminal coupled tothe first terminal of the current rate limiting circuit and the clampingdiode having a second terminal coupled to the input supply voltage; anda second clamping diode having a first terminal coupled to the firstterminal of the current rate limiting circuit and the second clampingdiode having a second terminal coupled to ground.